We use, and have with every litter we have had, a 16 X 22 Plastic Tub (see through) We put a heating pad in the bottom that is covered by usually 3 receiving blankets that are changed frequently. The pups are brought home from the Vet in this tub and spend usually there first 2 weeks in it. We run the heating pad on medium unless the pups decide that it is to worm for them in which case we turn it off. There is plenty of room for the pups to get off the heating pad if they want to, but not so much that they cant find there way back when they feel the need. We keep the lid pulled back a couple of inches for ventilation, otherwise the tub is covered. We also keep a rolled up towel or notted sox under the blankets for obstacles that the pups will have to crawl over to move around in the tub, to prevent swimmers. Works great for us, and not very expensive. We keep 2 so we have an extra just incase of one of the pups needing to go to the Vet or if we have a bigger litter. Have had as many as 6 pups in one tub, not crowded.